Emulsions of highly fluorinated organic compounds

ABSTRACT

Improved emulsions of highly fluorinated organic compounds. The emulsions comprise a highly fluorinated organic compound, an oil, that is not substantially surface active and not significantly water soluble, and a surfactant. They are characterized by a well-defined relationship in the relative amounts of the three components.

This application is a division of Ser. No. 07/187,854, filed Apr. 29,1988, now allowed as U.S. Pat. No. 5,171,755.

TECHNICAL FIELD OF THE INVENTION

This invention relates to improved emulsions of highly fluorinatedorganic compounds and to processes of making and using them. Moreparticularly, this invention relates to fluorocarbon-containingemulsions having acceptable particle size distributions both aftersterilization and in the presence of serum, being safe at high doses andin total exchanges and having good shelf stability at room temperature.These emulsions comprise a highly fluorinated organic compound, an oil,that is not substantially surface active and not significantly solublein water and a surfactant. The emulsions are characterized by a welldefined relationship in the relative amounts of these three components.Such emulsions are especially useful in compositions for use as oxygentransport agents, "artificial bloods", or red blood cell substitutes, inthe treatment of heart attack, stroke, and other vascular obstructions,as adjuvants to coronary balloon angioplasty and cancer radiationtreatment and chemotherapy and as contrast agents for biologicalimaging.

BACKGROUND OF THE INVENTION

Highly fluorinated organic compounds, such as perfluorocarbon compounds("PFC") are well known to be chemically and pharmaceutically inert. Theyalso have the capacity of dissolving, transporting and deliveringbiologically and chemically significant quantities of oxygen. Theseproperties make them potentially useful as oxygen transport agents,"artificial bloods" or red blood cell substitutes, in the treatment ofheart attack, stroke and other vascular obstructions, as adjuvants tocoronary angioplasty, cancer radiation treatment and chemotherapy and ascontrast agents for various biological imaging modalities, such asnuclear magnetic resonance, ultrasound, x-ray and positron emissiontomography.

Neat fluorocarbon liquids, however, cannot be injected into the bloodstream, because their hydrophobic character makes them immiscible in theblood. As a result, they may cause vascular obstruction and death whentransported into small blood vessels. Accordingly, for medical uses thatrequire intravascular injection, such highly fluorinated organicmolecules must be dispersed as physiologically acceptable, aqueousemulsions. See, e.g., L. C. Clark, Jr. et al., "Emulsions ofPerfluorinated Solvents for Intravascular Gas Transport", Fed. Proc.,34(6), pp. 1468-77 (1975); K. Yokoyama et al., "A PerfluorochemicalEmulsion as an Oxygen Carrier", Artif. Organs (Cleve), 8(1), pp. 34-40(1984); and U.S. Pat. Nos. 4,110,474 and 4,187,252.

To date the medical usefulness of such emulsions of highly fluorinatedorganic compounds as "artificial bloods", red blood cell substitutes,oxygen transport agents or contrast agents for biological imaging hasnot been as successful as hoped. This results from the fact that none ofthe prior fluorocarbon-containing emulsions satisfies all ofrequirements of a preferred "artifical blood" or oxygen transport agent.

These requirements include:

(1) Particle Size Distribution (PSD) Post Sterilization Less Than 400 nm

A critical parameter for stability and safety is the PSD of theemulsion. Extensive prior art literature demonstrates that a PSD >400 nmresults in excessive toxicity because the microcirculatory filters largeparticles leading to clogged microcirculatory vasculature and ultimatelygeneral ischemia. The particle size will also impact the rate ofclearance from the circulatory system and emulsions which are notmaintained in the circulatory system will not be efficacious as bloodsubstitutes. Because terminal heat sterilization of these emulsions isnecessary to eliminate the possibility of sepsis before use, emulsionswhich exhibit a PSD >400 run (post sterilization) are, thus, notacceptable.

(2) Serum Stability Characterized By A PSD <400 run After Five Days InSerum Or Ionic Solutions

Of great importance to a given emulsion formulation is stability to theserum environment. A lack of serum or ionic stability results inparticles that grow in vivo resulting in emboli that may clog themicrovasculature and may lead to paralysis and death. In addition to thecatastrophic growth that leads to death, modest in vivo particle growthresults in more rapid clearance from the circulatory system and hencereduced efficacy as a red blood cell substitute or oxygen transportagent. Accordingly, emulsions which exhibit a PSD >400 nm (after 5 daysin serum or ionic solutions) are not acceptable.

(3) Survival At High Doses

A major limitation to the use of an emulsion is the LD₅₀ or maximum safedose. Regulatory agencies limit the use level of an emulsion based onsome fraction of the LD₅₀. Emulsions which have a higher maximumallowable dose and, thus, can be used in higher, more effective dosagesand in a broader range of clinical applications will be more broadlyaccepted by the medical community. An acceptable emulsion should have anLD₅₀ in rats of at least 16 ml/kg of the perfluorocarbon component--theactive ingredient of the emulsion.

(4) Survival In Total Exchanges

Total exchange transfusions represent the most stringent test ofemulsion safety and efficacy. In a total exchange, the animal'shematocrit is reduced to 3% or less, a level which would be fatalwithout intervention. Simultaneously, the candidate emulsion isisovolumically infused. The animal's physiologic functions, survival,general appearance and health, and intravasculature persistence are thenmonitored. Emulsions which lead to a high level of survival are believedto have good safety and efficacy. An acceptable emulsion should have atleast a 70% survival rate in total exchanges in rats.

(5) Shelf Stability

A key criteria for the commercial utility of an emulsion is its shelfstability. Emulsions which cannot be stored for several months at either4° C., and more preferably 25° C., will not be useful in the field.Their shelf life will be too short with respect to the time lag betweenmanufacturing and quarantine, shipping, and usage.

In addition to these requirements, fluorocarbon-containing emulsionsthat are to be used as "artificial bloods" or "red blood cellsubstitutes" must deliver sufficient oxygen to the tissues of the body.

As is well known, blood oxygen is normally transported by hemoglobin, ahighly specialized protein that on-loads oxygen in the lungs andoff-loads oxygen in the tissues of the body. When atmospheric oxygen,which has an oxygen partial pressure (p0₂) of approximately 150 mm Hg,is breathed and is present in the alveoli of the lungs, the aterialblood p0₂ is about 100 mm Hg (because of the water vapor saturating thegas in the pulmonary alveoli, the bronchial circulation and othersources of arterio-venous shunting through the lungs)- At thisrelatively low p0₂ all of hemoglobin's carrier sites for oxygen arealmost completely saturated (97%). Thus, when the oxygen dissolved inthe arterial blood plasma is in equilibrium with the hemoglobin of wholeblood, 100 ml of that blood will carry about 20 ml of oxygen (20 volumepercent).

When this oxygen-carrying blood moves into the capillaries where itoff-loads its oxygen to the tissues, it comes into dynamic oxygenequilibrium with the oxygen present in the perivascular interstitialfluid, which on average has a p0₂ of 40 mm Hg. This difference in p0₂level between the arterial and the venous side of the circulationpermits delivery to the tissues of their normal requirement of about 5ml of oxygen per 100 ml of whole blood (5 volume percent).

In contrast to hemoglobin which actually binds and then releases oxygen,emulsions of highly fluorinated organic compounds merely dissolveoxygen. Accordingly, the amount of oxygen delivered by afluorocompound-containing emulsion depends on the difference between thearterial p0₂ and the venous p0₂, the solubility of oxygen in thefluorocarbon and the percentage (by volume) of the fluorocarbon in theemulsion: ##EQU1##

For use as an "artifical blood" or red blood cell substitute, afluorocompound-containing emulsion should deliver at least as muchoxygen as whole blood--5% by volume. At the 100% O₂ breathing mixtureused for up to 12 hours in critical care situations, such an emulsionshould, thus, contain at least about 20% by volume of thefluorocompound. E.g. (using the equation above):

desired O₂ delivery =5% (by volume)

arterial p0₂ =600 mm Hg (100% O₂)*

venous p0₂ =40 mm Hg

solubility of O₂ in fluorocompound=33% (by volume)**

percentage (by volume) of fluorocarbon required=x ##EQU2##

At the 40% to 80% O₂ breathing mixture tolerated for longer times than12 hours in hospital settings, such emulsion should contain from about25% to about 60% by volume of the fluorocarbon, and most preferably from30% to 55% by volume.

It is clear from the foregoing that without relatively high PFCcontents, perfluorocarbon emulsions will not be capable of deliveringthe quantities of oxygen that are available from whole blood.Compounding the oxygen delivery shortcomings of low % (by volume) PFCemulsions are two additional factors critical to the medical use ofperfluorocarbon emulsions. The first is the need for high oxygendelivery per unit volume of fluid administered. There is a limit to thevolume of fluid that can be delivered to a patient, especially if theheart or kidneys are suspected to be compromised. The second additionalshortcoming of low % (by volume) PFC emulsions is that in high volumetransfusions it is usually necessary to mix the infused emulsion withother solutions needed to support the ionic and oncotic needs of thepatient. Therefore, dilution of low % PFC emulsions with "annex"solutions containing salts and suitable plasma expanders serves todilute the already low oxygen delivery capacity of these formulations.

Illustrative of the deficiencies of prior fluorocarbon-containingemulsions is "Fluosol DA 20%", the only fluorocarbon emulsion to reachclinical testing as an "artificial blood". It is an about 10% (byvolume) emulsion of two fluorocarbons--perfluorodecalin andperfluorotripropylamine--in a mixture of two surfactants--egg yolkphospholipid and Pluronic F-68. It is not stable in the liquid state andmust be stored frozen (Yokoyama et al., supra). Furthermore, therequired presence of the perfluorotripropylamine in this emulsion, tohelp "stabilize" it, virtually eliminates the emulsion's medicalusefulness (as an artificial blood or oxygen transport agent) becausethe half-life of the perfluorotripropylamine in the liver and the otherbody tissues is longer than desirable (see, e.g., K. Yokoyama et al.,supra). Finally, because this emulsion contains only about 10%fluorocarbon by volume, it is much less therapeutically effective as an"artificial blood" than desired because of its low oxygen deliverycapacity--about 2.4% O₂ at 100% inspired oxygen (see, e.g., "Fluosol-DAAs A Red Cell Substitute In Acute Anemia", N.E. Jour. Med, 314, pp.1653-66 (1986)). This is substantially less than the 5 volume % oxygenwhich must be delivered to sustain healthy physiologic function.

Also illustrative of these deficiencies are the three fluorocarbonemulsions referred to in Jeppsson et al., "Particle Size Distribution OfA Fluorochemical Emulsion", in HS Symposium Research onPerfluorochemicals in Medicine and Biology, Huddinge, Sweden, Apr.28-29, 1977, Karolinska Institute Research Center, Proceedings,Novakova, et al., ed., pp. 108-113 (1978). These emulsions contain about15% (by volume) fluorocarbon--too little to be useful as an "artificialblood" or "red blood cell substitute"--a use, in fact, never evensuggested by Jeppsson.

One attempt to remedy the problems of these prior artfluorocarbon-containing emulsions is described in Shaw-Clark Europeanpatent application 231,091. The emulsions of that application arecharacterized by high fluorocarbon contents and good stability at roomtemperature and after sterilization. They comprise an oil that is notsubstantially, surface active and not significantly soluble in water, asurfactant and a highly fluorinated organic compound. Although a vastimprovement over prior emulsions, the genus of Shaw-Clark emulsionsinclude some that do not satisfy all of the other requirements describedabove for emulsions preferred for use as "artificial bloods", oxygentransport agents, or contrast agents for biological imaging.

Jeppsson (supra) also refers to oil, surfactant andfluorocarbon-containing emulsions. See, e.g., Jeppsson, supra, andEuropean patent applications 220,152 and 220,153. Jeppsson does notsuggest that its emulsions permit the preferred higher concentrations ofperfluorocarbons needed for "artificial bloods", oxygen transport agentsor contrast agents for biological imaging. Nor does Jeppsson suggestthat its emulsions satisfy the other requirements of preferred emulsionsfor use in these applications. In fact, the Jeppsson emulsions includemany that do not satisfy all of these other requirements of thepreferred emulsions described above.

SUMMARY OF THE INVENTION

This invention solves the problems referred to above. It provides forthe first time emulsions of highly fluorinated organic compounds thatsatisfy all of the requirements of the preferred emulsions describedabove.

The emulsions of this invention are characterized by (1) a particle sizedistribution after sterilization of less than about 400 nm, andpreferably less than about 300 nm; (2) a serum stability characterizedby a particle size distribution of less than 400 run, and preferablyless than 300 nm, after five days in serum or ionic solutions; (3) anLD₅₀ in rats of at least 16 ml/kg of the fluorocarbon component of theemulsion; (4) an at least 70% survival in total exchange in rats and (5)a shelf stability of at least several months at 4° C., and preferably at25° C.

The improved emulsions of this invention comprise at least one highlyfluorinated organic compound; an oil that is not substantially surfaceactive and not significantly soluble in water; and a surfactant. Moreimportantly, the emulsions of this invention are characterized byspecific and defined relationships in the relative amounts of thosethree components. The fluorocarbon component is present in the emulsionin an amount between about 10% and about 60% by volume. The amounts ofthe surfactant and the oil are dependent on the volume percent offluorocarbon and are defined by the volume depicted in FIG. 1 and by thesurfaces that define that volume.

This invention also includes methods of making these improved emulsionsand methods and compositions of using them as oxygen transport agents,"artificial bloods" or red blood cell substitutes, and contrast agentsfor biological imaging, and in other medical compositions andapplications known in the art.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three dimensional diagram--w/w % oil/fluorocarbon, w/w %surfactant/fluorocarbon, and vol % fluorocarbon-containing compound--ofthe improved emulsions of this invention. The volume depicted in FIG. 1and the surfaces defining it describe the improved emulsions of thisinvention. The filled-in circles in FIG. 1 represent emulsions of thisinvention that satisfy all of the requirements of the preferredemulsions described above. The open circles represent emulsions thatfail in one or more of those requirements.

DETAILED DESCRIPTION OF THE INVENTION

The emulsions of this invention comprise at least one highly fluorinatedorganic compound; an oil that is not substantially surface active andnot significantly soluble in water; and a surfactant.

The emulsions of this invention are stable at room temperature for longperiods of time--at least several months. They are stable to agitationand to mixing with various physiological additives, including, but notlimited to, saline, Tyrode solution, lactated Ringer's solution, serumand serum products. They exhibit substantially no phase separation andsubstantially no change in particle size or droplet distribution duringstorage. Moreover, they permit the use of highly fluorinated organiccompounds that exhibit acceptably rapid excretion times from the liverand other body tissues. And they permit the use of high concentrationsof fluorocarbons, thereby producing the high oxygen delivery capacityemulsions required for use as therapeutically effective bloodsubstitutes, oxygen transport agents and contrast agents for biologicalimaging. Because of their stability, they retain the above-mentionedproperties even after sterilization in a conventional laboratoryautoclave at 121° C. for fifteen minutes.

Among the highly fluorinated organic compounds that are useful in theemulsions and processes of this invention are those previously said tobe useful as oxygen transport agents, "artificial bloods" or red cellsubstitutes, and contrast agents for biological imaging. These includeperfluorocarbons, e.g., perfluorodecalin, perfluoroindane,perfluorotrimethylbicyclo[3.3.1]-nonane, perfluoromethyladamantane,perfluorodimethyladamantane, and perfluoro-2,2,4,4-tetramethylpentane;9-12 C perfluoroamines, e.g., perfluorotripropylamine,perfluorotributylamine, perfluoro-1-azatricyclic amines; bromo- or iodo-substituted fluorocarbons: and F-4-methyloctahydroquinolidizine andperfluoroethers. Such compounds are described, for example, in U.S. Pat.Nos. 3,962,439, 3,493,581, 4,110,474, 4,186,253, 4,187,252, 4,252,827,4,423,077, 4,443,480, 4,534,978 and 4,542,147, European patentapplications 80,716 and 158,996, British patent specification 1,549,038,and German Offen. 2,650,586. Of course, it should be understood thatmixtures of any of these highly fluorinated organic compounds may alsobe used in the emulsions and processes of this invention.

Preferably, the emulsions of this invention contain one or more of aperfluorocarbon and more preferably a perfluorocarbon selected from thegroup consisting of perfluorodecalin, perfluoromethyladamantane,perfluorodimethyladamantane, perfluorooctylbromide,perfluoro-4-methyloctahydroquinolidizine,perfluoro-N-methyldecahydroquinoline, F-methyl-1-oxa-decalin,perfluoro-bicyclo[5.3.0]decane, perfluorooctahydroquinolidizine,perfluoro-5,6-dihydro-5-decene, and perfluoro-4,5-dihydro-4-octene. Mostpreferably, the perfluorocarbon is perfluorodecalin orperfluorooctylbromide. For use as a contrast agent for biologicalimaging, perfluorooctylbromide is the preferred highly fluorinatedorganic compound according to this invention.

While the highly fluorinated organic compounds, or mixture of suchcompounds, may comprise from about 10% to about 60% (by volume) of theemulsions, the preferred emulsions of this invention employconcentrations of at least about 20% to about 60% (by volume) of thehighly fluorinated organic compound. More preferably, the emulsions ofthis invention comprise from about 30% to about 55% (by volume)fluorocarbon. Most preferably, the emulsions contain 40% by volume.

Among the not substantially surface active and not significantly watersoluble oils that are useful in the emulsions and processes of thisinvention are liquid fatty oils, hydrocarbons, waxes, such as monoestersof a fatty acid and a monohydroxy alcohol, long chain ethers,diglycerides, silicone oils and nitriles. These include, for example,palmitoyl oleate, octyl nitrile, dodecyl nitrile, soybean oil, saffloweroil, hexadecane, diglycerides having a C₁₂ -C₁₈ carbon chain, andmineral oil. As with the fluoro-containing component, these oils may beused singly or in various combinations in the emulsions and processes ofthis inventon.

When the emulsions of this invention are to be used medically, the oilor combination of oils must, of course, be physiologically acceptable.For example, when our emulsions are to be used as "artificial bloods" ortherapeutically as oxygen transport agents or contrast agents, wepreferably use physiologically acceptable liquid fatty oils, such assoybean and safflower oils.

Among the surfactants useful in the emulsions of this invention are anyof the known anionic, cationic, nonionic and zwitterionic surfactants.These include, for example, anionic surfactants such as alkyl or arylsulfates, sulfonates, carboxylates or phosphates, cationic surfactantssuch as mono-, di-, tri-, and tetraalkyl or aryl ammonium salts,nonionic surfactants, such as alkyl or aryl compounds, whose hydrophilicmoiety consists of polyoxyethylene chains, sugar molecules, polyalcoholderivatives or other hydrophilic groups that may be combinations of theabove anionic or cationic groups, and whose hydrophobic moiety consistsof any other polymer, such as polyisobutylene or polypropylene oxides.Again, combinations of these surfactants may, of course, be used in theemulsions of this invention. In addition, mixtures of compounds, one ormore of which are not surfactants, but which compounds when combined actas surfactants, may also be usefully employed as the surfactantcomponent of the emulsions of this invention.

Again, when the emulsions of this invention are to be used in"artificial bloods" or therapeutically as oxygen transport agents orcontrast agents, the surfactant, or combinations of them, must bephysiologically acceptable. For example, for such uses we prefernonionic or zwitterionic surfactants. Preferably, the surfactants usedin the emulsions of this invention are one or more of the following: eggand soybean phosphatides, lecithin, and any of the series of BASFWyandotte formulations of polyoxyethylene oxides sold under the tradename "Pluronic", especially "Pluronic F-68". Of course, many otherpolyethylene oxide based surfactants can be employed, but they are nottypically as accessible through common channels of commerce.

In addition to the highly fluorinated organic compounds, oils, andsurfactants, the emulsions of this invention contain water and may alsocontain, or be mixed with, other components conventionally used in"artificial bloods" or red blood cell substitutes, oxygen transportagents or contrast agents for biological imaging. These include isotonicagents, osmotic pressure controlling agents, serum extending agents andantioxidants. For example, we have successfully incorporated glycerol asa tonicity adjusting agent during the preparation of these emulsions toobtain solutions of physiologically acceptable osmolarities. The properamounts to obtain isotonicity with respect to whole blood will beobvious to those skilled in the art. In addition, we have shown that,after preparation and heat sterilization, these emulsions may be mixedwith 0.9% saline, lactated Ringer's solution, serum and serum productswith no adverse affect on emulsion particle size and stability. Otheradjuvants can also be used in the emulsions of this invention. Amongthem are oncotic agents such as dextran, HES, and antioxidants.

The emulsions of this invention are characterized by a well-definedrelationship in the relative amounts of the fluorocarbon, oil andsurfactant components. This specific relationship or interdependence inbest depicted and described by reference to FIG. 1.

In FIG. 1 the emulsions of this invention are defined as a volume on athree-dimensional plot of w/w % oil/fluorocarbon, w/w %surfactant/fluorocarbon, and % volume fluorocarbon. Emulsions fallingwithin this volume, or on the surfaces defining it, are within the scopeof this invention. Emulsions falling outside of this described volumeand these surfaces are, correspondingly, not part of this invention.

Using FIG. 1, then, one of skill in the art can readily select the rangeof oils and the range of surfactants useful at a particular volume %fluorocarbon to prepare the emulsions of this invention. Morepreferably, one of skill in the art can select a particular oil andsurfactant amount within that defined range for use in preparing anemulsion of this invention.

Although FIG. 1 is based on emulsions prepared withperfluorodecalin,-egg yolk lecithin and safflower oil, we believe thatother combinations of fluorocarbons, oils and surfactants, as describedabove, will display a similar interdependence of components. However, itshould be understood that slightly different volumes and surfaces maydefine the actual interrelationship of the components of those otheremulsions. It is plainly within the skill of the art based on theteachings of this application to determine those exact volumes andsurfaces without undue experimentation and without departing from thescope and teachings of this invention.

In the more preferred emulsions of this invention, the fluorocarbon isperfluorodecalin, the surfactant is egg yolk lecithin, and the oil issafflower oil. In the most preferred emulsions of this invention, theperfluorodecalin is present in about 40% by volume, the lecithin presentin about 2.3 w/w % lecithin/PFD and the safflower oil present in about2.6 w/w % oil/PFD.

The emulsions of this invention may be prepared using any order ofmixing the three components and water. However, we prefer to mix the oilfirst with a water dispersion of the surfactant. We then prepare thefinal emulsion by adding the fluorocarbon.

The mixing and emulsification of the components of the emulsions of thisinvention may be done with any of the mechanical homogenizers incommercial use, and do not require the use of extravagant equipment suchas ultrasonic homogenizers, although such equipment may be used inlaboratory scale production. We prefer to use an inert atmosphere toprevent degradation of the surfactant and fatty oils and to usetemperatures, preferably between about 45° and 55° C. to decrease theviscosity of the material being emulsified.

In order that this invention be more fully understood, we have includedthe following illustrative examples. These examples do not limit theforegoing disclosure of this invention.

EXAMPLES PROCEDURES Preparation Of Aqueous Lecithin Dispersion

Powdered, refined, egg yolk lecithin was obtained from Kabi Vitrum anddispersed in sterile H₂ O under an inert atmosphere (N₂) using a Waring™Blender at high speed for 2 minutes. The blended material wastransferred to a reservoir, again under an inert atmosphere, which fed aMicrofluidizer™ Model 110 homogenization apparatus. The material wascycled through the homogenizer at a flow rate of 350 ml/min, using 60psig air pressure to drive the pump piston, for a total of 5 minutes.The temperature was maintained below 25° C. throughout. In this manner,approximately 750 g lots were prepared, at concentrations ranging from10 to 27%. The lecithin so dispersed was collected under an inertatmosphere and stored at 4° C. All lecithin dispersions so prepared wereused within one week of their preparation.

Preparation of Emulsion

The emulsifier reservoir was first loaded with the appropriate charge ofsterile water, glycerol, and lecithin dispersion described above. Theemulsifier was then started, and the oil was added via a syringe pump ata flow rate of from 10-30 ml/min directly into the inlet port of thehomogenizer. The perfluorocarbon was then added via syringe pump at thesame flow rate into the same port. The temperature was maintained at45°-48° C. throughout, and the pH was maintained at 7.5-8.5 bycontrolled addition of 0.29M NarCO₃ or other base. For a 250-ml batch,the material was cycled through the homogenizer at a flow rate of300-350 ml/min for 10 minutes. Proportionately longer mean residencetimes were used for larger batch sizes (e.g., for a 500-ml batch, aresidence time of 20 minutes was employed).

ANALYSIS Particle Size Distribution Analysis (PSD)

Samples were analyzed according to published operating procedures on aBrookhaven BI-90 Particle Sizer. All samples were prepared in isotonicglycerol solution immediately prior to the analysis.

Serum Stability (PSD)

Samples were diluted 1:1 with a 4:1 mixture of lactated Ringer'ssolution and 25% human serum albumin (HSA), buffered to pH 7.2 with aphosphate buffer. Samples were incubated at 37° C. for 120 hrs. beforeparticle size distribution analysis.

Total Exchange

Doubly cannulated rats (jugular vein/carotid artery) were isovolumicallyexchanged according to Goodin et al., "A Method For Evaluation Of BloodSubstitutes In The Conscious Animal", Am. Jour. Physiol., 245, H519-523(1983) until the hematocrit was approximately 3%. The initial FiO₂ of0.8 was reduced daily at 0.1 increments over a 4-day span, after whichthe animals were returned to room air. Survival was scored at 14 days.

LD₅₀ Analysis

The test emulsion (50 ml/kg of a 4:1 mixture of stem emulsion (40% byvolume PFC) and annex (equivalent to 16 ml/kg of fluorocarboncomponent)) is infused at a rate of 1 ml/kg via the tail vein of 10140-200g Sprague-Dawly rats lightly anasthetized with ether. Afterinfusion, the animals are returned to their cage and supplied with foodand water ad libitum. After 14 days the survival rate is scored. Testemulsions of other PFC volume percents would be prepared similarly toadduce 16 ml/kg of fluorocarbon component.

Shelf Stability

The test emulsions are stored in stoppered 100 ml serum bottles under anitrogen atmosphere at 4° C. or 25° C. for at least three months. Afterstorage, the samples are tested for particle size distribution (laserlight scattering), pH, and visual quality (color, creaming, etc.).

SPECIFIC EMULSIONS

Forty-seven different emulsions were prepared in duplicate by themethods outlined in the procedures section. Each emulsion containedperfluorodecalin, safflower oil and egg yolk lecithin. The actualconcentrations of the components of these emulsions are described inTable I. The emulsions were then analyzed as above. The results arereported in Table II and plotted in FIG. 1--open circle for those thatfailed one or more requirements and filled-in circle for those thatsatisfied all requirements.

                  TABLE I                                                         ______________________________________                                        Ex.     Lec/PFD       Saf/PFD  PFD %                                          No.     (w/w %)       (w/w %)  (v/v)                                          ______________________________________                                         1      0.66%         2.6%     30.0%                                           2      1.15%         13.0%    30.0%                                           3      2.08%         17.4%    30.0%                                           4      2.60%         0.7%     30.0%                                           5      2.60%         2.6%     30.0%                                           6      2.60%         5.2%     30.0%                                           7      3.99%         10.1%    30.0%                                           8      6.08%         6.1%     30.0%                                           9      6.08%         13.9%    30.0%                                          10      7.99%         4.0%     30.0%                                          11      8.68%         5.2%     30.0%                                          12      8.68%         17.4%    30.0%                                          13      9.03%         4.0%     30.0%                                          14      9.03%         8.0%     30.0%                                          15      1.30%         0.0%     40.0%                                          16      1.30%         1.3%     40.0%                                          17      1.30%         4.6%     40.0%                                          18      1.30%         7.2%     40.0%                                          19      1.30%         13.0%    40.0%                                          20      1.95%         2.6%     40.0%                                          21      1.95%         5.2%     40.0%                                          22      1.95%         7.8%     40.0%                                          23      1.95%         10.4%    40.0%                                          24      2.60%         2.6%     40.0%                                          25      2.93%         2.6%     40.0%                                          26      2.93%         5.2%     40.0%                                          27      2.93%         7.8%     40.0%                                          28      2.93%         10.4%    40.0%                                          29      3.91%         1.3%     40.0%                                          30      3.91%         3.9%     40.0%                                          31      3.91%         6.5%     40.0%                                          32      3.91%         10.4%    40.0%                                          33      4.60%         1.3%     40.0%                                          34      4.60%         13.0%    40.0%                                          35      5.20%         0.0%     40.0%                                          36      5.99%         3.9%     40.0%                                          37      7.81%         0.0%     40.0%                                          38      7.81%         1.3%     40.0%                                          39      7.81%         7.2%     40.0%                                          40      7.81%         13.0%    40.0%                                          41      9.11%         2.6%     40.0%                                          42      7.81%         2.6%     50.0%                                          43      2.60%         2.6%     50.0%                                          44      0.66%         2.6%     50.0%                                          45      2.60%         0.7%     50.0%                                          46      2.60%         5.2%     50.0%                                          47      5.21%         2.6%     50.0%                                          ______________________________________                                    

                  TABLE II                                                        ______________________________________                                                       PSD                                                                           (nM)                Survival                                   Ex.*    PSD    Serum     Survival**                                                                              Total                                      No.     (nM)   120 h     (16 ml/kg PFC)                                                                          Exchange                                   ______________________________________                                         1      487    554                                                             2      409    1262                                                            3      285    564                                                             4      269    267                                                             5      221    230                                                             6      235    242                                                             7      205    223                                                             8      270    245                                                             9      280    276                                                            10      279    254                                                            11      290    240                                                            12      474    429                                                            13      388    377                                                            14      338    320                                                            15      363    460                                                            16      290    436       90%        0%                                        17      269    427                                                            18      314    1163                                                           19      435    1592      70%       33%                                        20      221    366                                                            21      219    --                                                             22      245    400                                                            23      269    916                                                            24      207    327       95%       83%                                        25      178    319                                                            26      172                                                                   27      213    410                                                            28      202    511                                                            29      277    274                                                            30      220    247                                                            31      259    255                                                            32      327    511                                                            33      239    206                                                            34      655    705                                                            35      235                                                                   36      320    287                                                            37      219                                                                   38      379    306       --        100%                                       40      595    838        0%       67%                                        41      318    307                                                            42      373    342                                                            43      324    325                                                            44      503    612                                                            45      290    286                                                            46      428    427                                                            47      300    324                                                            ______________________________________                                         *All emulsions (1-47) had a greater than three month shelf stability at       room temperature as measured by particle size distribution analysis and       visual inspection.                                                            **A percent survival at 16 ml/kg PFC of less than 50% corresponds to an       LD.sub.50 of less than 16 ml/kg PFC.   ** A percent survival at 16 ml/kg      PFC of less than 50% corresponds to an LD.sub.50 of less than 16 ml/kg     PFC. ** A percent survival at 16 ml/kg PFC of less than 50% corresponds to     an LD.sub.50 of less than 16 ml/kg PFC.

While we have hereinbefore described a number of embodiments of ourinvention, it should be apparent that other embodiments also existwithin our invention. Therefore, it should be understood that the scopeof this invention is to be defined by the claims rather than by thespecific embodiments which have been presented hereinbefore by way ofexample.

We claim:
 1. A contrast agent for biological imaging comprising aphysiologically acceptable emulsion in an amount clinically effectivefor imaging by modalities selected from the group consisting of nuclearmagnetic resonance, x-ray, ultrasound and positron emission tomography,wherein the emulsion comprises a highly fluorinated organic compound, anoil that is not substantially surface active and not significantly watersoluble, and a surfactant, and wherein(a) the highly fluorinated organiccompound is present in the emulsion in an amount between about 20% andabout 60% by volume and (b) the amounts of the surfactant and oil in theemulsion are dependent on the volume percent of highly fluorinatedorganic compound and are present in amounts effective to produceemulsions characterized by (1) a particle size distribution of less than400 nm after sterilization, (2) a serum stability characterized by aparticle size distribution of less than 400 nm after 5 days in serum orionic solutions, (3) an LD₅₀ in rats of at least 16 ml/kg of the highlyfluorinated organic compound component of the emulsion, (4) an at least70% survival upon total exchange in rats, and (5) a shelf stability ofat least several months at 4° c.
 2. A contrast agent for biologicalimaging comprising a physiologically acceptable emulsion in an amountclinically effective for imaging by modalities selected from the groupconsisting of nuclear magnetic resonance, x-ray, ultrasound and positronemission tomography, wherein the emulsion comprises a highly fluorinatedorganic compound, an oil that is not substantially surface active andnot significantly water soluble, and a surfactant, and wherein(a) thehighly fluorinated organic compound is present in the emulsion in anamount between about 20% and about 60% by volume and (b) the amounts ofthe surfactant and oil in the emulsion are dependent on the volumepercent of highly fluorinated organic compound and are present inamounts effective to produce emulsions characterized by (1) a particlesize distribution of less than 300 nm after sterilization, (2) a serumstability characterized by a particle size distribution of less than 300nm after 5 days in serum or ionic solutions, (3) an LD₅₀ in rats of atleast 16 ml/kg of the highly fluorinated organic compound component ofthe emulsion, (4) an at least 70% survival upon total exchange in rats,and (5) a shelf stability of at least several months at 25° C.
 3. Thecontrast agent according to claim 1 or 2, wherein the highly fluorinatedorganic compound is present in the emulsion in an amount between about30% and about 55% by volume.
 4. The contrast agent according to claim 1or 2, wherein the highly fluorinated organic compound is present in theemulsion in about 40% by volume.
 5. The contrast agent according toclaim 1 or 2, wherein the highly fluorinated organic compound isselected from the group consisting of perfluorooctylbromide andperfluorodecalin.
 6. The contrast agent according to claim 1 or 2,wherein the oil is selected from the group consisting of safflower oiland soybean oil.
 7. The contrast agent according to claim 1 or 2,wherein the surfactant is egg yolk lecithin.
 8. The contrast agentaccording to claim 1 or 2, further comprising at least one compoundselected from the group consisting of isotonic agents, osmotic pressurecontrolling agents, serum extending agents and antioxidants.
 9. A methodfor non-invasive imaging of internal organs and bloodflow comprising thestep of administering to a patient in a pharmaceutically acceptablemanner a contrast agent selected from the contrast agents of claims 1 or2 in conjunction with an imaging modality selected from magneticresonance imaging, ultrasound, positron emission tomography and x-ray.